It is well known in the manufacture of multi-layered products, such as resilient floor, wall or ceiling coverings, or resilient desk, table or counter tops, and the like, that it is often necessary to bond together two or more layers of dissimilar synthetic polymeric materials and that it is often difficult to obtain a strong and permanent bond between such dissimilar synthetic materials.
Such difficulties often are believed to arise in the bonding of such dissimilar synthetic polymeric materials because of the differences in surface energies. For example, if atoms from two dissimilar synthetic polymeric materials cannot get close enough to each other, perhaps because of large dissimilarities or disparities in polarity, van der Waals forces cannot be adequately taken advantage of to create strong permanent bonding. Nor is it believed that hydrogen bonding can be adequately taken advantage of in such situations. Many proposals have been made to overcome such difficulties and to improve the bond between such dissimilar synthetic polymeric materials but none has been found to be completely satisfactory to date.
The present invention will be described with particular reference to the bonding of vinyl resins and polyurethane or acrylated polyurethane resins and it is to be appreciated that the principles of the present invention are applicable to all vinyl resins and polyurethane or acrylated polyurethane resins. Similarly, the present invention will be described with specific reference to multi-layered products, such as, for example, resilient floor coverings utilizing these dissimilar synthetic polymeric materials but again, it is to be appreciated that the principles of the present invention are equally applicable to other multi-layered products which also utilize such dissimilar synthetic polymeric materials.
In the manufacture of resilient floor coverings, normally a relatively flat base layer or substrate is laid out in substantially horizontal condition. Such a base layer or substrate is customarily a felted or matted fibrous sheet of overlapping, intertwined fibers and/or filaments, usually of asbestos or of natural, synthetic or man-made cellulosic origin, although many other forms of sheets and films or textile materials or fabrics may be used.
Upon this substantially flat, horizontal base layer or substrate is then applied a substantially uniform base layer of a liquid or semi-liquid resinous composition which contains a synthetic polymeric material, usually an ungelled polyvinyl chloride plastisol, usually containing a blowing or foaming agent. This liquid or semi-liquid plastisol composition is subsequently gelled at an elevated temperature to a relatively firm condition by procedures which are conventional and well known in the art. This relatively firm, gelled plastisol may then be printed with a decorative multi-colored pattern or design in which certain predetermined areas contain a blowing or foaming inhibitor which subsequently modifies the action of the blowing or foaming agent in those certain predetermined area. Several different printing ink compositions may be used.
A substantially uniform wear layer usually of a clear liquid or semi-liquid resinous composition and usually containing another ungelled polyvinyl chloride plastisol composition but generally not containing any blowing or foaming agent is then applied as a wear resistant coating to the surface of the base layer of printed, firmed and gelled polyvinyl chloride plastisol and is subsequently firmed and gelled thereon, either as a separate operation or in a joint operation with a subsequent fusing and blowing and foaming operation of the base layer of polyvinyl chloride plastisol. Thus far, there is relatively very little difficulty in creating a strong, permanent bond or adhesion between the base layer of polyvinyl chloride plastisol and the wear layer, which is also a polyvinyl chloride plastisol.
It is then frequently desired to provide a top surface coating to the surface of the polyvinyl chloride wear layer and it is often desired that such top surface coating be a polyurethane or acrylated polyurethane resin, primarily because of their superior physical and chemical properties and characteristics. However, in many instances, it is found that the adhesion or bond between the vinyl resin wear layer and the polyurethane or acrylated polyurethane resin top surface coating is not as strong or as permanent, as desired or required. It is believed that such lack of strength and of permanency or lack of suitable resistance to delamination is due to the fact that the wear layer and the top surface coating are dissimilar synthetic polymeric materials.